The present invention relates to an ophthalmic lens comprising an antireflective stack which strongly reduces reflection in the UV range and in the visible range. The antireflective stack comprises composite high index layers.
In the past few years, anti-UV function has been greatly emphasized due to the increasing concern on eye protection against ultra violet (UV) light. In particular, UV light coming from back or side of wearer should not be reflected towards wearer's eyes by the rear face of ophthalmic lenses. A very efficient antireflective property in the ultraviolet light range is required. This property is easily measured by Ruv, the mean reflection factor between 280 nm and 380 nm, weighted by the function W(λ) defined in the ISO 13666:1998 standard. In the same time, a very efficient antireflective property in the visible range is required for the front face of the lens to avoid ghosts and cosmetically unpleasant reflected light. This property is easily measured by Rv, the mean reflection factor as defined in the ISO 13666:1998 standard.
Unfortunately, when a stack is designed to minimize Ruv, Rv is usually too high. And when a stack is designed with a very low Rv, Ruv is usually not satisfying. The balance between Ruv and Rv should be improved.
Inventors surprisingly discovered that using composite high index layers enables design of very efficient antireflective stack simultaneously for Ruv and Rv.
Composite layers have been already used in antireflective stacks for various industries. U.S. Pat. No. 4,260,222 discloses three layered antireflective stacks in which a single composite layer of zirconium oxide and tantalum oxide is used. This composite layer is deposited in high temperature conditions, which are not suitable for organic ophthalmic lenses, and its composition provides a better uniformity of refractive index. However, antireflective performance in UV range is not considered, and is actually bad.
European patent EP1211524 discloses four layered antireflective stacks for ophthalmic lenses in which high index layers are composite layers of Titanium oxide, Niobium oxide and zirconium oxide, providing improved mechanical and chemical characteristics to the antireflective stack. niobium oxide and titanium oxide are required as main components, in amount larger than 25% for niobium oxide. Actually, performance in UV range is not demonstrated.